Volkner (Japanese: デンジ Denzi) is the Gym Leader of Sunyshore City's Gym, known officially as the Sunyshore Gym. He hands out the Beacon Badge to Trainers who defeat him. He specializes in Electric-type Pokémon.

Volkner uses Electric-type Pokémon in his battles. Trainers who defeat him will receive the Beacon Badge, TM57 (Charge Beam) and will be able to use Waterfall outside of battle. Volkner is friends with Flint, and has become dejected because no worthy challengers have come to Sunyshore in a while. He has been considering challenging the Elite Four and spends all his time renovating the Gym's electrical equipment, which puts a strain on Sunyshore's power supply and causes a blackout. When the player arrives in Sunyshore, Flint introduces them to Volkner, who agrees to hold off on challenging the Elite Four until after he battles the new challenger.

In Pokémon Platinum, Volkner and Flint appear at the entrance to the Battle Frontier and have a double battle against the player and their rival.

Pokémon
Pokémon Diamond and Pearl
His team consists of the following Pokémon:

At Vista Lighthouse
"... ... ...so you're the latest challenger up against the Sunyshore Gym...All right, I've decided! If I find you to be weak, I'm going to challenge the Pokémon League. I'm all done with renovating the Gym, so I don't need to be here. More than anything, I want to have battles that can thrill me again.As the toughest Gym Leader in Sinnoh, I'm going to unleash everything in my arsenal on you."

Before battle
"...all right, challenger. It's not often, but some Trainers manage to come and challenge me. But they've all been boring battles. I didn't break a sweat beating them. ...Sigh... I'm Volkner, the Gym Leader. They say I'm the top Gym Leader in Sinnoh, but... Anyway, I guess we'd better get this done. I hope you're the Trainer who'll make me remember how fun it is to battle!

After sending out last Pokémon
"Here it comes! Get ready for my trump card!

During battle
"Shocking... I didn't see this coming!"

When defeated
"You've got me beat... Your desire and the noble way your Pokémon battled for you... I even felt thrilled during our match. That was a very good battle."

After being defeated
"...hehehe. Hahahah! ...That was the most fun I've had in a battle since...I don't know when! It's also made me excited to know you and your team will keep battling to greater heights! This is your eighth badge. You've earned this!

Volkner bears a startling resemblance to Minato Namikaze from the popular franchise Naruto.
All of Volkner's Diamond and Pearl Pokémon are Pokémon that have gender differences.
Two of Volkner's Pokémon in Diamond and Pearl are not of his chosen type, Electric (Ambipom is a Normal-type and Octillery is a Water-type, a strange choice as Water is weak against Electricity). However, each of these Pokémon knows one Electric-type move (Shock Wave and Charge Beam respectively). This changed in Platinum when Ambipom and Octillery's places where taken by Jolteon and Electivire.
Volkner's Electivire is the only Pokémon of a Gym Leader to use seals in Pokémon Platinum. Coincidentally, it is used in the double battle with Flint, who uses his Magmortar, the only Pokémon of a member of the Elite Four to have seals.

Japanese デンジ (Denzi) Means electromagnetic (電磁 denji).
English, German Volkner Probably derived from German name "Volker" for "defender". Sounds similar to volt.
French Tanguy Probably from the term "tension électrique" (electrical tension), usually referred to in English as "voltage".
Italian Corrado From corrente, current.
Spanish Lectro From eléctrico, electric.
Korean 전진 Jeonjin May be a combination of 'lightning' (電, jeon) and 'thunder' (震, jin).